The invention is particularly applicable in the field of aeronautics where knowledge of the angle of attack of a flow of air surrounding an aircraft is essential to the piloting of the aircraft. The angle of attack with respect to a horizontal plane of the aircraft is an important parameter for determining the lift of the aircraft and particularly when close to stalling. The angle of attack with respect to a vertical plane of the aircraft is also important; this corresponds to the yaw of the aircraft. In order to determine these two parameters—angle of attack and yaw—the orientation of the airflow on the skin of the aircraft can be measured locally. These are local measurements of angles of attack that are carried out at particular points of the aircraft.
Three large families of aerodynamic probes have been developed for measuring the local angle of attack on the aircraft.
A first family of probe uses a mobile appendage protruding from the skin of the aircraft. This mobile appendage can take the form of a flag oriented along the axis of the airflow. The orientation of the flag then gives the local angle of attack of the airflow. These mobile probes must comprise systems for rotation between fixed and mobile parts with minimum friction.
A second family of probe uses an appendage having two orifices activating a pneumatic motor closed-loop controlling the said appendage in such a manner that the two pressures remain equal.
A third family of probe uses a fixed appendage protruding from the skin of the aircraft. The determination of the local angle of attack may be effected based on a differential measurement between two pressure sampling ports disposed on the nose of the fixed appendage, one situated on the leading edge of the appendage and the other on the trailing edge. The leading edge and the trailing edge are defined with respect to a region of the appendage where the airflow forms a null point with a zero angle of attack. This method for determining the local angle of attack has several drawbacks. In order to obtain a high enough precision, notably during certain phases of flight, the gain of the measurement chain must be high enough and saturation of the latter is quickly reached. Moreover, for high angles of attack, the airflow detaches from the appendage, thus causing errors in the measurement of a local angle of attack.
Other principles have been proposed: measurement by LIDAR or completely mechanical systems.